Adhesive composition, optical member, and surface protective sheet

ABSTRACT

An adhesive composition includes a copolymer (A), the copolymer (A) being a copolymer of: a hydroxyl group-containing (meth)acrylamide (a1), the hydroxyl group-containing (meth)acrylamide (a1) including at least one of a hydroxyl group-containing acrylamide and a hydroxyl group-containing methacrylamide, and a (meth)acrylate (a2), the (meth)acrylate (a2) including at least one of an acrylic ester and a methacrylic ester; and an antistatic agent (B), the antistatic agent (B) including an ionic compound.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of pending International ApplicationNo. PCT/KR2008/006501, entitled “Adhesive Composition, and OpticalMember, Surface Protective Sheet,” which was filed on Nov. 4, 2008, theentire contents of which are hereby incorporated by reference.

BACKGROUND

1. Field

The present invention relates to adhesive compositions, optical members,and surface protective sheet.

2. Related Art

As in cathode ray tubes, a surface of a flat display panel also tends tobe charged with static electricity. When the surface of the flat displaypanel is charged with the static electricity, dust in air can often beattracted to a display plane of the panel. Further, the staticelectricity can have a negative influence on a display circuit of asubstrate constituting the flat display panel or on orientation ofliquid crystal molecules in the panel, thereby causing displaymalfunction.

When examining display performance of the flat display panel, it isnecessary to remove a surface protective film which can cause opticalobstruction. To remove the surface protective film, the surfaceprotective film is peeled off at a rate of about 10 m/min to reduce aprocess time. Such a relatively high rate of peeling off the surfaceprotective film causes the display plane to be easily charged with thestatic electricity.

SUMMARY

It is a feature of an embodiment to provide an adhesive composition,which may have a short aging time resulting in high productivity andpermit the formation of an adhesive layer exhibiting good antistaticperformance, and an optical member and surface protective filmcomprising the same.

It is another feature of an embodiment to provide an optical member thatincludes the adhesive composition coated on one or both sides of anoptical sheet, thereby providing a short aging time resulting in highproductivity, while exhibiting good antistatic performance.

It is another feature of an embodiment to provide a surface protectionsheet that includes a protective film and an adhesive layer comprisingthe adhesive composition on one or both sides of the protective film,thereby providing a short aging time resulting in high productivity,while exhibiting good antistatic performance.

At least one of the above and other features and advantages may berealized by providing an adhesive composition, including: a copolymer(A), the copolymer (A) being a copolymer of: a hydroxyl group-containing(meth)acrylamide (a1), the hydroxyl group-containing (meth)acrylamide(a1) including at least one of a hydroxyl group-containing acrylamideand a hydroxyl group-containing methacrylamide, and a (meth)acrylate(a2), the (meth)acrylate (a2) including at least one of an acrylic esterand a methacrylic ester; and an antistatic agent (B), the antistaticagent (B) including an ionic compound.

The hydroxyl group-containing (meth)acrylamide (a1) may be representedby the following formula: H₂C═C(R1)ACONHCH₂CH₂OH, in which R1 is H orCH₃, A is a linking group, the linking group being (COOCH₂CH₂)_(n),COOCH₂CH₂OOC—CH₂CH₂, a single bond, or Compound 1 represented byChemical Formula 1:

and

n is 1 or 2.

The adhesive composition may be for an optical member, and the copolymer(A) may include about 0.1 to about 5% by weight of the hydroxylgroup-containing (meth)acrylamide (a1) based on a total weight of thecopolymer (A).

The adhesive composition may be for a surface protection sheet, and thecopolymer (A) may include about 0.1 to about 10% by weight of thehydroxyl group-containing (meth)acrylamide (a1) based on a total weightof the copolymer (A).

The copolymer (A) may include about 50 to about 99.1% by weight of the(meth)acrylamide (a2) based on a total weight of the copolymer (A).

The (meth)acrylamide (a2) may include at least one of methyl(meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl(meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl(meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl(meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate,n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, methoxyethyl(meth)acrylate, ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate,phenoxyethyl (meth)acrylate, nonylphenoxy polyethylene glycol(meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, andtetrahydrofurfuryl (meth)acrylate.

The adhesive composition may be for an optical member, and the copolymer(A) may include about 80 to about 99.89% by weight of n-butyl acrylateas the (meth)acrylamide (a2) based on a total weight of the copolymer(A).

The adhesive composition may be for an optical member, and the copolymer(A) may include about 0.1 to about 5% by weight ofhydroxyethylacrylamide as the hydroxyl group-containing (meth)acrylamide(a1) based on a total weight of the copolymer (A).

The copolymer may be for a surface protective film, and the copolymer(A) may include about 50 to about 99.89% by weight of2-ethylhexylacrylate as the (meth)acrylamide (a2) based on a totalweight of the copolymer (A).

The adhesive composition may be for an optical member, and the basepolymer (A) may have a polystyrene conversion weight-average molecularweight of about 1,000,000 to about 2,000,000 as determined by gelpermeation chromatography.

The adhesive composition may be for a surface protection sheet, and thebase polymer (A) may have a polystyrene conversion weight-averagemolecular weight of about 300,000 to about 1,000,000 as determined bygel permeation chromatography.

The base polymer (A) may have a glass transition temperature (Tg) ofabout 0° C. or less.

The ionic compound may include at least one of an imidazolium salt, apyridinium salt, an alkyl ammonium salt, an alkyl pyrrolidium salt, andan alkyl phosphonium salt.

The copolymer (A) may be crosslinked.

The adhesive composition may be for an optical member, and the copolymer(A) may have a gel fraction of about 50 to about 80% as a crosslinkingdegree.

The adhesive composition may be for a surface protection sheet, and thecopolymer (A) may have a gel fraction of about 90 to about 100% as acrosslinking degree.

The adhesive composition may include about 0.01 to about 2.0% by weightof the antistatic agent (B).

At least one of the above and other features and advantages may also berealized by providing an optical member, including an optical sheet, andan adhesive layer, the adhesive layer being formed by coating theadhesive composition according to an embodiment on one or both sides ofthe optical sheet.

The adhesive layer may have a sheet resistance of about 1×10⁸ to about1×10¹¹ Ω/cm².

At least one of the above and other features and advantages may also berealized by providing a surface protection sheet, including a protectivefilm, and an adhesive layer formed on one or both sides of theprotective film, the adhesive layer including the adhesive compositionaccording to an embodiment.

The adhesive layer may have a sheet resistance of about 1×10⁸ to about1×10¹¹ Ω/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of skill in the art by describing in detail example embodimentswith reference to the attached drawings, in which:

FIGS. 1 through 8 illustrate Tables 1 through 8, respectively.

DETAILED DESCRIPTION

Japanese Patent Application No. 2007-302702, filed on Nov. 22, 2007, inthe Japanese Patent Office, and entitled: “Adhesive Composition, andOptical Member, Surface Protective Sheet,” is incorporated by referenceherein in its entirety.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Adhesive Composition

According to an embodiment, an adhesive composition includes a copolymer(A) and an antistatic agent (B). The copolymer (A) may be formed bycopolymerization of a hydroxyl group-containing (meth)acrylamide (a1)and a (meth)acrylate (a2). The hydroxyl group-containing(meth)acrylamide (a1) may include a hydroxyl group-containingacrylamide, a hydroxyl group-containing methacrylamide, or acombinations thereof. The (meth)acrylate (a2) may include an acrylicester, a methacrylic ester, or a combination thereof. The antistaticagent (B) may include an ionic compound.

The base polymer (A), i.e., the copolymer (A), may be crosslinked by acrosslinking agent. In an example embodiment, the antistatic agent maybe added to the base polymer (A) so that an adhesive layer formed bycoating the adhesive composition on a substrate such as optical sheetsor protective films has a surface resistance of, for example, about1×10⁸ to about 1×10¹¹ Ω/cm².

Base Polymer

According to this embodiment, the base polymer may be formed bycopolymerization of: (hereinafter, referred to as the “hydroxylgroup-containing (meth)acrylamide (a1)”) hydroxyl group-containingacrylamides, hydroxyl group-containing methacrylamides, or combinationsthereof; and (hereinafter, referred to as the “(meth)acrylate (a2)”)acrylic esters, methacrylic esters, or combinations thereof.

When using the adhesive composition according to this embodiment for anoptical member, the base polymer (A) may contain about 0.1 to about 5wt. % of the hydroxyl group-containing (meth)acrylamide (a1) based on atotal weight of the base polymer (A). If the amount of the hydroxylgroup-containing (meth)acrylamide (a1) is less than about 0.1 wt. % inthe base polymer (A), there is a possibility of insufficiently enhancingthe antistatic performance. If the amount of the hydroxylgroup-containing (meth)acrylamide (a1) exceeds about 0.5 wt. % in thebase polymer (A), there is a possibility of providing insufficientdurability.

Further, when using the adhesive composition according to thisembodiment for a surface protection sheet, the base polymer (A) maycontain about 0.1 to about 10 wt. % of the hydroxyl group-containing(meth)acrylamide (a1) based on a total weight of the base polymer (A).

If the amount of the hydroxyl group-containing (meth)acrylamide (a1) isless than about 0.1 wt. % in the base polymer (A), there is apossibility of insufficiently enhancing the antistatic performance. Ifthe amount of the hydroxyl group-containing (meth)acrylamide (a1)exceeds about 10 wt. % in the base polymer (A), there is a possibilityof providing insufficient adhesion to the protective film orinsufficient transparency to the adhesive layer.

Examples of the hydroxyl group-containing (meth)acrylamide (a1) includeH₂C═C(R1)ACONHCH₂CH₂OH (where R1 represents H or CH₃, and A represents alinking group). The linking group may be, e.g., a single bond. Thelinking group may be, e.g., (COOCH₂CH₂)_(n) or COOCH₂CH₂OOC—CH₂CH₂,which may be bonded via terminal carbons thereof, and in which n may be1 or 2. The linking group may be, e.g., Compound 1 represented by thefollowing Chemical Formula 1, which may be bonded via a terminal carbonand a carbon of the aromatic ring.

The hydroxyl group-containing (meth)acrylamide (a1) may includehydroxyethyl acrylamide (HEAA) and the like.

The (meth)acrylate (a2) may be a main element of the base polymer (A),e.g., it may be present in an amount of about 50 to about 99.1 wt. %based on a total amount of the base polymer (A). The base polymer (A)may include a single (meth)acrylate (a2), or may include two or more(meth)acrylates (a2).

Examples of the (meth)acrylate (a2) include methyl (meth)acrylate, ethyl(meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl(meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate,isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl(meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate,n-tetradecyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl(meth)acrylate, butoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate,t-butylcyclohexyl (meth)acrylate, phenoxyethyl (meth)acrylate,nonylphenoxy polyethylene glycol (meth)acrylate, benzyl (meth)acrylate,isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and thelike.

It is desirable that the base polymer (A) of the adhesive compositionfor the optical member contain n-butyl acrylate as a main element of the(meth)acrylate in order to realize high adhesion.

Further, it is desirable that the base polymer (A) of the adhesivecomposition for the surface protection sheet contain 2-ethylhexylacrylate as a main element of the (meth)acrylate (a2) to exhibit adegree of adhesion that allows easy separation of the surface protectionsheet.

The base polymer (A) may be an acrylate polymer that includes one ormore of the (meth)acrylates (a2) as main elements, since the acrylatepolymer has good compatibility with ionic compounds and provides goodadhesive properties.

When using the adhesive composition of this embodiment for the opticalmember, the base polymer (A) may have a weight-average molecular weightof about 1,000,000 to about 2,000,000. When the weight-average molecularweight of the base polymer (A) is in the range of about 1,000,000 toabout 2,000,000, the adhesive composition may provide a sufficientadhesive force as a composition constituting an adhesive layer of theoptical member.

The weight-average molecular weight of the base polymer (A) can beobtained by polystyrene conversion and gel permeation chromatography.

Further, the base polymer (A) may have a glass transition temperature Tgof about 0° C. or less. In an implementation, the base polymer (A) mayhave a glass transition temperature Tg of about −100 to about −5° C.,and more advantageously a glass transition temperature Tg of about −80to about −10° C. If the glass transition temperature Tg is less than orequal to about 0° C., the adhesive composition may provide a higheradhesive force when containing an ionic compound.

In another implementation, the base polymer (A) may contain othercomponents besides, i.e., in addition to or instead of, the hydroxylgroup-containing (meth)acrylamide (a1) and the (meth)acrylate (a2).

The other components of the base polymer may include components forenhancing cohesive force and thermal resistance, such as sulfonic acidgroup-containing monomers, phosphoric acid group-containing monomers,cyano group-containing monomers, vinyl esters, aromatic vinyl compounds,and the like, or components having functional groups capable ofenhancing the adhesive force or capable of acting as a crosslinkstarter, such as carboxyl group-containing monomers, acid anhydridegroup-containing monomers, hydroxyl group-containing monomers, amidegroup-containing monomers, amino group-containing monomers, epoxygroup-containing monomers, N-acryloyl morpholine, vinyl ethers, and thelike. The other components may be used alone or in combination of two ormore kinds of components.

Examples of the sulfonic acid group-containing monomers may includestyrene sulfonic acid, allyl sulfonic acid,2-(meth)acrylamido-2-methylpropane sulfonic acid, methacrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, and the like.

An example of the phosphoric acid group-containing monomers may include2-hydroxyethyl acryloyl phosphate.

An example of the cyano group-containing monomers may includeacrylonitrile.

An example of the vinyl esters may include vinyl acetate.

An example of the aromatic vinyl compounds may include styrene.

Examples of the carboxyl group-containing monomers may include(meth)acrylic acid, carboxyethyl(meth)acrylate,carboxypentyl(meth)acrylate, itaconic acid, maleic acid, crotonic acid,2-carboxyethyl acrylate, and the like.

Examples of the acid anhydride group-containing monomers include maleicanhydride, itaconic anhydride, and the like.

Examples of the hydroxyl group-containing monomers may include2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate,8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate,12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methylacrylate, N-methylol (meth)acrylamide, vinyl alcohol, allyl alcohol,2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethyleneglycolmonovinyl ether, and the like.

Examples of the amide group-containing monomers may include acrylamide,diethyl acrylamide, and the like.

Examples of the amino group-containing monomers may includeN,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, and the like.

Examples of the epoxy group-containing monomers may include glycidyl(meth)acrylate, allylglycidyl ether, and the like.

An example of the vinyl ethers may include vinyl ethyl ether.

Examples of a method of polymerizing the base polymer (A) may includesolution polymerization, emulsion polymerization, bulk polymerization,suspension polymerization, and the like.

For the polymerization of the base polymer (A), a polymerizationinitiator may be used. Examples of the polymerization initiator mayinclude peroxides such as benzoyl peroxide, lauroyl peroxide, and thelike; and azobis compounds such as azobisisobutyronitrile (AIBN),azobisvaleronitrile, and the like.

Crosslinking Agent

In an example embodiment, the adhesive composition may be crosslinked,which may provide an adhesive layer having excellent thermal resistance.The base polymer (A) may be crosslinked, e.g., at the acrylic polymer(a2), which may be the main element of the base polymer (A).

Crosslinking may be conducted by a method using a crosslinking agent inwhich a compound containing a group is added to react with a carboxylgroup, a hydroxyl group, an amino group, an amide group, or the likecontained as a crosslinking starter in an acrylic polymer such as onecontaining isocyanate compounds, epoxy compounds, aziridine compounds,and/or metal chelate compounds.

Examples of the isocyanate compounds may include aromatic diisocyanatessuch as tolylene diisocyanate and xylene diisocyanate; alicyclicdiisocyanates such as isophoron diisocyanate; and aliphatic isocyanates,such as hexamethylene diisocyanate. In particular, the isocyanatecompounds or the epoxy compounds may be used in view of their cohesiveproperties. These compounds may be used alone or in a combination of atleast two kinds.

More specifically, examples of the isocyanate compounds may include: lowaliphatic polyisocyanates such as butylene diisocyanate andhexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylenediisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate;aromatic isocyanates such as 2,4-tolylene diisocyanate,4,4′-diphenylmethane diisocyanate, and xylylene diisocyanate; andisocyanate adducts such as a trimethylolpropane/tolylene diisocyanatetrimer adduct (trademark: Coronate L), atrimethylolpropane/hexamethylene diisocyanate trimer adduct (trademark:Coronate HL), and an isocyanurate product of hexamethylene diisocyanate(trademark: Coronate HX) (all manufactured by Nippon PolyurethaneIndustry Co., Ltd.).

Examples of the epoxy compounds may includeN,N,N′,N′-tetraglycidyl-m-xylenediamine (trademark: TETRAD-X) and1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (trademark: TETRAD-C) (allmanufactured by Mitsubishi Gas Chemical Co., Inc.).

These crosslinking agents may be used alone or in a combination of twoor more kinds. The content of the crosslinking agent may be selectedaccording to balance with a crosslinking target base polymer, andaccording to applications of the optical member. To achieve sufficientthermal resistance by the cohesive force of the acrylate adhesive agent,the content of the crosslinking agent may be about 0.01 parts by weightor more based on 100 parts by weight of the base polymer. Further, inview of flexibility and adhesion, the content of the crosslinking agentmay be about 0.05 parts by weight or less based on 100 parts by weightof the base polymer.

When the adhesive composition according to this embodiment is used forthe optical member, the base polymer (A) of the adhesive composition mayhave a gel fraction of about 50 to about 80% as a crosslinking degree,and more advantageously a gel fraction of about 70% as a crosslinkingdegree, which may help increase the adhesive force of the adhesivecomposition.

When the adhesive composition according to this embodiment is used forthe surface protection sheet, the base polymer (A) of the adhesivecomposition may have a gel fraction of about 90 to about 100% as acrosslinking degree, whereby the adhesive force of the adhesivecomposition may be decreased so as to facilitate the separation of thesurface protection sheet.

The gel fraction may be obtained from an initial mass of the adhesivecomposition (before digestion) and a mass thereof after immersing anddrying in the case where the adhesive composition is immersed in ethylacetate at 25° C. for 1 day, as calculated by Equation: GelFraction=[Mass after immersing and drying/Initial Mass]×100.

Antistatic Agent

The antistatic agent may include an ionic compound.

The ionic compound may be selected to have compatibility with the basepolymer and an organic solvent used in the preparation of the adhesivecomposition, while allowing transparency of the adhesive composition tobe maintained when the ionic compound is added to the base polymer.Further, the ionic compound may be selected to have a surface resistanceof about 1×10¹¹ Ω/cm² or less when the adhesive composition is appliedto a substrate such as the optical sheet or the protective film.

The ionic compound may include one or more of an imidazolium salt, apyridinium salt, an alkyl ammonium salt, an alkyl pyrrolidium salt, andan alkyl phosphonium salt.

Examples of the imidazolium salt include 1,3-dimethylimidazoliumchloride, 1-butyl-2,3-dimethylimidazolium chloride,1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazoliumchloride, 1-butyl-3-methylimidazolium methane sulfonate,1-butyl-1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-imidazoliumhexafluorophosphate, 1-ethyl-3-methylimidazolium bromide,1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazoliumhexafluorophosphate, 1-ethyl-3-methylimidazolium iodide,1-ethyl-2,3-dimethylimidazolium chloride, 1-methylimidazolium chloride,1,2,3-trimethylimidazolium methyl sulfate,1-methyl-3-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-imidazoliumhexafluorophosphate, 1-aryl-3-methylimidazolium chloride,1-benzyl-3-methylimidazolium chloride, 1-benzyl-3-methylimidazoliumhexafluorophosphate, 1-benzyl-3-methylimidazolium tetrafluorophosphate,and the like.

Examples of the pyridinium salt include 1-butyl-3-methylpyridiniumbromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-4-methylpyridiniumchloride, 1-butylpyridinium bromide, 1-butylpyridinium chloride,1-butylpyridinium hexafluorophosphate, 1-ethylpyridinium bromide,1-ethylpyridinium chloride, and the like.

Examples of the alkyl ammonium salt include cyclohexyltrimethylammoniumbis(trifluoromethylsulfonyl)imide, tetra-n-butylammonium chloride,tetrabutylammonium bromide, tributylmethylammonium methylsulfate,tetrabutylammonium bis(trifluoromethylsulfonyl)imide, tetraethylammoniumtrifluoromethanesulfonate, tetrabutylammonium benzoate,tetrabutylammonium methanesulfate, tetrabutylammoniumnonafluorobutanesulfonate, tetra-n-butylammonium hexafluorophosphate,tetrabutylammonium trifluoroacetate, tetrahexylammoniumtetrafluoroborate, tetrahexylammonium bromide, tetrahexylammoniumiodide, tetraoctylammonium chloride, tetraoctylammonium bromide,tetraheptylammonium bromide, tetrapentylammonium bromide,n-hexadecyltrimethylammonium hexafluorophosphate, and the like.

Examples of the alkyl pyrrolidium salt include1-butyl-3-methylpyrrolidium bromide, 1-butyl-1-methylpyrrolidiumchloride, 1-butyl-1-methylpyrrolidium tetrafluoroborate, and the like.

Examples of the alkyl phosphonium salt include tetrabutylphosphoniumbromide, tetrabutylphosphonium chloride, tetrabutylphosphoniumtetrafluoroborate, tetrabutylphosphonium methanesulfonate,tetrabutylphosphonium p-toluenesulfonate, tributylhexadecylphosphoniumbromide, and the like.

For the ionic compound, a nitrogen-containing onium salt, asulfur-containing onium salt, or a phosphorous-containing onium salt maybe used.

Examples may include 1-butylpyridinium tetrafluoroborate,1-butylpyridinium hexafluorophosphate, 1-butyl-3-methylpyridiniumtetrafluoroborate, 1-butyl-3-methylpyridinium trifluoromethanesulfonate,1-butyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide,1-butyl-3-methylpyridinium bis(pentafluoroethanesulfonyl)imide,1-hexylpyridinium tetrafluoroborate, 2-methyl-1-pyrrolintetrafluoroborate, 1-ethyl-2-phenylindole tetrafluoroborate,1,2-dimethylindole tetrafluoroborate, 1-ethylcarbazoletetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate,1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazoliumtrifluoroacetate, 1-ethyl-3-methylimidazolium heptafluorobutyrate,1-ethyl-3-methylimidazolium trifluoromethanesulfonate,1-ethyl-3-methylimidazolium perfluorobutanesulfonate,1-ethyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazoliumbis(pentafluoroethanesulfonyl)imide, 1-ethyl-3-methylimidazoliumtris(trifluoromethanesulfonyl)methide, 1-butyl-3-methylimidazoliumtetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium trifluoroacetate,1-butyl-3-methylimidazolium heptafluorobutyrate,1-butyl-3-methylimidazolium trifluoromethanesulfonate,1-butyl-3-methylimidazolium perfluorobutanesulfonate,1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazoliumchloride, 1-hexyl-3-methylimidazolium tetrafluoroborate,1-hexyl-3-methylimidazolium hexafluorophosphate,1-hexyl-3-methylimidazolium trifluoromethanesulfonate,1-octyl-3-methylimidazolium tetrafluoroborate,1-octyl-3-methylimidazolium hexafluorophosphate,1-hexyl-2,3-dimethylimidazolium tetrafluoroborate,1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide,1-methylpyrazolium tetrafluoroborate, 3-methylpyrazoliumtetrafluoroborate, tetrahexylammoniumbis(trifluoromethanesulfonyl)imide, diallyldimethylammoniumtetrafluoroborate, diallyldimethylammonium trifluoromethanesulfonate,diallyldimethylammonium bis(trifluoromethanesulfonyl)imide,diallyldimethylammonium bis(pentafluoroethanesulfonyl)imide,N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate,N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammoniumtrifluoromethanesulfonate,N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammoniumbis(trifluoromethanesulfonyl)imide,N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammoniumbis(pentafluoroethanesulfonyl)imide, glycidyltrimethylamoniumtrifluoromethanesulfonate, glycidyltrimethylamoniumbis(trifluoromethanesulfonyl)imide, glycidyltrimethylammoniumbis(pentafluoroethanesulfonyl)imide, 1-butylpyridinium(trifluoromethanesulfonyl)trifluoroacetamide, 1-butyl-3-methylpyridinium(trifluoromethanesulfonyl)trifluoroacetamide,1-ethyl-3-methylimidazolium(trifluoromethanesulfonyl)trifluoroacetamide,diallyldimethylammonium(trifluoromethanesulfonyl)trifluoroacetamide,glycidyltrimethylammonium(trifluoromethanesulfonyl)trifluoroacetamide,N,N-dimethyl-N-ethyl-N-propylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-butylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-ethyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-hexylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-ethyl-N-heptylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-nonylamoniumbis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N,N-dipropylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-propyl-N-butylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-propyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-propyl-N-hexylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-propyl-N-heptylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-butyl-N-hexylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-butyl-N-heptylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dimethyl-N-pentyl-N-hexylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N,N-dihexylammoniumbis(trifluoromethanesulfonyl)imide, trimethylheptylammoniumbis(trifluoromethanesulfonyl)imide,N,N-diethyl-N-methyl-N-propylammoniumbis(trifluoromethanesulfonyl)imide,N,N-diethyl-N-methyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide,N,N-diethyl-N-methyl-N-heptylammoniumbis(trifluoromethanesulfonyl)imide,N,N-diethyl-N-propyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide, triethylpropylammoniumbis(trifluoromethanesulfonyl)imide, triethylpentylammoniumbis(trifluoromethanesulfonyl)imide, triethylheptylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dipropyl-N-methyl-N-ethylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dipropyl-N-methyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dipropyl-N-butyl-N-hexylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dipropyl-N,N-dihexylammoniumbis(trifluoromethanesulfonyl)imide,N,N-dibutyl-N-methyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide, N,N-dibutyl-N-methyl-N-hexylammoniumbis(trifluoromethanesulfonyl)imide, trioctylmethylammoniumbis(trifluoromethanesulfonyl)imide, andN-methyl-N-ethyl-N-propyl-N-pentylammoniumbis(trifluoromethanesulfonyl)imide, and the like.

Ingredient Ratio of Base Polymer (A) and Antistatic Agent (B)

An ingredient ratio of the antistatic agent (B) with respect to a totalamount of the base polymer (A) and antistatic agent (B) may be about0.01 wt. % to about 2 wt. %. If the ingredient ratio is less than about0.01 wt. %, a sufficient antistatic effect may not be obtained, whereasif the ingredient ratio exceeds about 2 wt. %, there is a possibility ofcontamination of an attachment target.

Other Additives

The adhesive composition may further contain other additives forproviding adhesive properties. For example, a surface lubricant, aleveling agent, an antioxidant, an anti-corrosion agent, a lightstabilizer, an ultraviolet absorbing agent, a polymerization inhibitor,a silane coupling agent, an inorganic or organic filler, a metal powder,a pigment powder, or a particle or foil-shaped material may beappropriately added according to intended use.

Preparation Method of Adhesive Composition

Examples of a method of preparing the adhesive composition according toan embodiment may include the following two methods.

In one method, a variety of monomers, which are the raw materials of thebase polymer (A), are mixed with an organic solvent having a boilingpoint of 120° C. or less, such as ethyl acetate, toluene, acetone,hexane, ketones, and alcohols, and are polymerized by the addition of apolymerization initiator, thereby preparing the base polymer. The basepolymer may be, e.g., a random copolymer. The obtained base polymer maybe in a dissolved state or expanded in the organic solvent.

Next, an antistatic agent, which may include one or more ioniccompounds, is added to the organic solvent containing the base polymerto be mixed with the base polymer.

Subsequently, a crosslinking agent is added to crosslink the basepolymer, and additives such as the silane coupling agent and the likeare further added as needed. As a result, the adhesive composition maybe prepared.

The adhesive composition obtained is applied to a substrate such as theoptical sheet or the surface protective film, and dried, thereby formingan adhesive layer on the substrate.

In another method, a variety of monomers, which are the raw materials ofthe base polymer (A), are mixed with an organic solvent such as ethylacetate while adding the antistatic agent consisting of the ioniccompounds thereto at the same time, and are then polymerized by theaddition of the polymerization initiator, thereby preparing the basepolymer containing the antistatic agent. As in the above method, thebase polymer obtained may be in a dissolved state or expanded in theorganic solvent.

Next, the crosslinking agent is added to the organic solvent containingthe base polymer and the antistatic agent to crosslink the base polymer,and the additives such as the silane coupling agent and the like arefurther added as needed. As a result, the adhesive composition may beprepared.

As in the above method, the obtained adhesive composition is applied tothe substrate such as the optical sheet or the surface protective filmand dried, thereby, forming the adhesive layer on the substrate.

As described above, when preparing the adhesive composition according tothis embodiment, the antistatic agent may be added after the preparationof the base polymer, or may be added while preparing the base polymer.In order to uniformly add the antistatic agent to the base polymer, theantistatic agent is advantageously soluble in the organic solvent suchas ethyl acetate.

Optical Member

An optical member according to an embodiment may be formed by coatingthe adhesive composition according to the embodiment of the invention onone or both sides of an optical sheet. For the optical member accordingto this embodiment, an adhesive layer containing the adhesivecomposition may be formed to a thickness of about 3 to about 200 μm, andadvantageously about 10 to about 100 μm, on one or both sides of theoptical sheet. The formation of the adhesive layer may be achieved bydirectly coating the adhesive composition on the optical sheet or bycoating the adhesive composition on a separate substrate (such as aseparation liner or the like) and transferring the coated adhesivecomposition to the optical sheet.

As a method of forming the adhesive layer, any known method used forpreparing an adhesive tape may be used. Specifically, examples of themethod include roll coating, gravure coating, reverse coating, rollbrushing, spray coating, air-knife coating, die-coat methods, and thelike.

According this embodiment, a variety of optical sheets for use inmanufacture of a variety of displays may be used without being limitedto a specific optical sheet. Examples of the optical sheet include apolarizer, a phase difference plate, a brightness enhancing plate, and aglare reducing sheet. Further, the optical sheet according to thisembodiment may be obtained by stacking two or more optical materials,such as a stack of the polarizer and the phase difference plate, a stackof the polarizers, a stack of phase difference plates, a stack of thepolarizer and the brightness enhancing plate or the glare reducingsheet, and the like.

The adhesive layer (adhesive composition) formed on the optical sheetmay have an adhesive force of about 1 (N/25 mm) to about 15 (N/25 mm),and more advantageously an adhesive force of about 5 (N/25 mm) to about10 (N/25 mm). When the adhesive force is in the range of 1 (N/25 mm) toabout 15 (N/25 mm), it will be sufficient for the adhesive layer of theoptical member. The adhesive force can be measured according to JISZ0237, which regulates a method for testing an adhesive tape and anadhesive sheet. In more detail, an optical member having an adhesivelayer may be evaluated for adhesive force by the following process: theoptical member may be left for seven days at 23° C. under a relativehumidity of 50%, cut into a width of 25 mm, autoclaved at 50° C. and at5 kg/cm²×20 min in a state of being adhered to, for example, thepolarizer; and measured for adhesive force at 23° C. under a relativehumidity of 50% using a tensile tester at a peeling angle of 180 degreesand at a peeling rate of 0.3 m/min according to JIS Z0237.

Surface Protection Sheet

A surface protection sheet for an optical member according to anembodiment may include a protective film and an adhesive layer formed onone or both sides of the protective film, in which the adhesive layerincludes the adhesive composition according to an embodiment. Theadhesive layer of the adhesive composition may be formed to a thicknessof about 3 to about 200 μm, and advantageously about 10 to about 100 μm,on one or both sides of the protective film.

Examples of the protective film may include resin films, such aspolyethylene terephthalate, polyethylene, polypropylene,ethylene-acetate vinyl copolymer, polyester, polyvinyl chloride,polycarbonate, polyamide, polystyrene films, and combinations thereof.Advantageously, a polyethylene terephthalate film may be used. Theprotective film may have a thickness of, for example, about 15 to about20 μm.

The formation of the adhesive layer on the protective film may beachieved by directly coating the adhesive composition on the protectivefilm, or by coating the adhesive composition on a separate substrate(such as a separation liner or the like) and transferring the coatedadhesive composition to the protective film.

As a method of forming the adhesive layer, any known method used forpreparing an adhesive tape may be used. Specifically, examples of themethod include roll coating, gravure coating, reverse coating, rollbrushing, spray coating, air-knife coating, die-coat methods, and thelike.

The surface protection sheet according to this embodiment may be used toprotect an optical member attached to a typical flat display panel suchas a liquid display panel, a plasma display panel, and the like.

The surface protection sheet according to this embodiment may be usednot only in the case where the optical member is individuallydistributed in the market, but also in the case where the optical memberis distributed in the market in a state of being attached to the flatdisplay panel.

The adhesive layer (adhesive composition) formed on the protective filmmay have an adhesive force of about 0.05 (N/25 mm) to about 0.2 (N/25mm), and more advantageously an adhesive force of about 0.1 (N/25 mm).When the adhesive force is in the range of about 0.05 to about 0.2 (N/25mm), the surface protection sheet may be relatively easily peeled fromthe optical member, such as a polarizer, at a rate of, for example,about 10 m/min. The adhesive force may be measured according to JISZ0237, which is described above.

The adhesive composition according to this embodiment may include thecopolymer (A), which may be formed by the copolymerization of thehydroxyl group-containing (meth)acrylamide (a1) (which may include ahydroxyl group-containing acrylamide, a hydroxyl group-containingmethacrylamide, and combinations thereof) and the (meth)acrylate (a2)(which may include an acrylic ester, a methacrylic ester, andcombinations thereof); and an antistatic agent (B) including an ioniccompound. The adhesive composition according to this embodiment may havea short aging time resulting in high productivity and may enable theformation of an adhesive layer exhibiting good antistatic performance.

Specifically, when the adhesive composition of this embodiment isapplied to the substrate such as the optical sheet or the protectivefilm to form an adhesive layer thereon, the adhesive layer may have asheet resistance of about 1×10⁸ to about 1×10¹¹ (Ω/cm²), and may exhibitgood antistatic performance.

Without being bound by theory, it is believed that, in the adhesivecomposition, the improvement of the antistatic performance is achievedas movement of the ionic compound in the adhesive layer is facilitatedby the presence of lone electron pair of nitrogen atoms contained in thehydroxyl group-containing acrylamide and/or the methacrylamide. Also,the short aging time of the adhesive composition of this embodiment ispresumably attributed to activation of the terminal hydroxyl group ofthe copolymer by the hydroxyl group-containing acrylamide and/or themethacrylamide, thereby increasing reactivity of the copolymer.

The adhesive composition of this embodiment may be very transparentwhere the base polymer contains at least one kind of (meth)acrylate as amain element.

When the base polymer of the adhesive composition has a weight-averagemolecular weight of about 1,000,000 to about 2,000,000 and a gelfraction of about 50 to about 80%, the adhesive composition may have ahigh adhesive force, and thus may be used to form the adhesive layer ofthe optical member.

When the base polymer of the adhesive composition has a weight-averagemolecular weight of about 300,000 to about 1,000,000 and a gel fractionof about 90 to about 100%, an adhesive layer on a surface protectionsheet formed by coating the adhesive composition may exhibit a weakadhesive force. In this case, the adhesive layer may be relativelyeasily peeled off, for example, at a rate of 10 m/min, from a displaysurface of a polarizer on a flat display panel.

EXAMPLES

Hereinafter, embodiments will be described with reference to Examples 1to 16.

Adhesive compositions according to Examples 1 to 16 were prepared andapplied to polarizers, thereby producing optical members of Examples 1to 16. Then, the optical members were tested for performance. A detaileddescription follows.

(Preparation of Copolymer Composition According to Example 1)

1 part by weight of hydroxyethylacrylamide as the (meth)acrylamidehaving a hydroxyl group, 98.99 parts by weight of butyl acrylate, and120 parts by weight of ethyl acetate as a solvent were introduced into aflask equipped with a reflux condenser and an agitator, and were heatedto 65° C. while conducting nitrogen substitution. Then, 0.04 parts byweight of AIBN as a polymerization initiator was added thereto, followedby polymerization for six hours at 65° C. When the polymerization wascompleted, 0.01 parts by weight of 1-hexyl-3-methylimidazoliumhexafluorophosphate as an ionic compound was added, and 280 parts byweight of ethyl acetate was further added to adjust viscosity, followedby cooling to room temperature, thereby producing a copolymercomposition solution containing the adhesive composition of Example 1.

The adhesive composition in the copolymer composition solution had aconcentration of 20 wt. %, and the copolymer composition solution had aviscosity of 4,500 mPa·s. Table 1 shows an ingredient ratio of theadhesive composition, a concentration of the adhesive composition in thecopolymer composition solution, and a viscosity of the copolymercomposition solution.

Further, the weight-average molecular weight of the base polymer wasmeasured by Gel Permeation Chromatography (GPC). Results are shown inTable 1.

(Preparation of Copolymer Composition Solutions According to Examples 2to 16)

Copolymer composition solutions containing adhesive compositions ofExamples 2 to 16 were obtained by the same process as that of Example 1,except for the following: at least one of butylacrylate, 2-ethylhexylacrylate, N,N-diethylacrylamide, 2-hydroxyethylacrylate,4-hydroxybutylacrylate, acrylic acid and acryl amide withhydroxyethylacrylamide combined (not combined) therewith as the hydroxylgroup-containing (meth)acrylamide was appropriately combined with ethylacetate as a solvent, while combining (not combining) one of1-hexyl-3-methylimidazolium hexafluorophosphate,N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide,1-ethylpyridinium bromide, 1-butyl-3-methylpyridiniumtrifluoromethanesulfonate, and 1-butyl-3-methylpyridiniumbis(trifluoromethanesulfonyl)imide as an ionic compound therewith at thesame time. Tables 1 and 2 show the ingredient ratios of the adhesivecompositions of Examples 2 to 16, the viscosity of each copolymercomposition solution, the concentration of the adhesive composition ineach copolymer composition solution, and the average weight molecularweight of the base polymer.

(Preparation of Optical Members of Examples 1 to 16)

With respect to 100 parts by weight of the adhesive composition in eachof the copolymer composition solutions of Examples 1 to 16 listed inTables 1 and 2, trimethylolpropane/tolylene diisocyanate (Trademark:Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd) as acrosslinking agent (B) and 3-glycidoxypropyltrimethoxysilane (Trademark:Shin-Etsu Silicone KBM-403, manufactured by Shin-Etsu Chemical IndustryCo., Ltd.) as a silane coupling agent (C) were added at the ratioslisted in Tables 3 and 4 and sufficiently mixed to prepare adhesivecomposition solutions. Each of the adhesive composition solutionsobtained was applied to a separable PET film (Trademark: MRF 38,manufactured by Mitsubishi Polyester Film Co., Ltd.) to a thickness of25 μm after drying, and dried at 90° C. for 3 minutes to form anadhesive layer consisting of the adhesive composition. Then, theadhesive layers and the separable PET films were attached to polarizers(Trademark: MLPH, manufactured by Migwan Imaging Co., Ltd.), therebyproducing optical members of Examples 1 to 16, respectively.

Performance of each optical member was tested for surface resistance,metal corrosiveness, light leakage, durability, viscosity, adhesion tosubstrate, contamination of attachment target, low temperaturestability, and reworkability. The performance test was carried out asdescribed below.

Further, the concentration of the adhesive composition in each adhesivecomposition solution and the viscosity of each adhesive compositionsolution were measured. Furthermore, the gel fraction and the period forobtaining a stabilized gel fraction were evaluated. Results are shown inTables 3 and 4.

Gel Fraction

Test samples 1 to 16 were prepared with polyester films having beenpeeled off, instead of the polarizers used in the preparation of theoptical members of Examples 1 to 16, and left at 23° C. under a relativehumidity of 50%, followed by measuring the gel fractions of the testsamples after 1, 3, 5, 7, 10, and 15 days from application.

The gel fraction is calculated by Equation: Gel fraction (wt.%)=[(W3−W2)/W1]×100

In this equation, W1 indicates the weight (g) of an adhesive layerobtained from a test sample. W2 indicates the weight (g) of a stainlesssteel wire mesh mentioned below. W3 indicates the total weight (g) ofthe stainless steel wire mesh and a layer on the wire mesh (remnantsafter filtering), which was obtained by the following process: 30 g ofethyl acetate was added to a sample container having the adhesive layerobtained from the test sample, and, after the adhesive layer wasimmersed therein overnight, the contents in the sample container werefiltered using a 200-mesh stainless steel wire mesh, and dried at 90° C.for one hour.

Period for Obtaining a Stabilized Gel Fraction

As described above, the gel fraction of each test sample was measuredafter a predetermined period from the application, and the period forwhich the gel fraction became steady was defined as a period forobtaining a stabilized gel fraction, or a gel fraction stabilizingperiod.

<Method of Performance Test>

Surface Resistance

The adhesive layers of the optical members, which had been left at 23°C. under a relative humidity of 50% for seven days, were measured forsurface resistance by a micro-electrometer (available from KawaguchiDenki Manufacturing Co., Ltd.) at 23° C. under a relative humidity of50%.

Metal Corrosiveness

An aluminum foil was attached to the adhesive layer of each opticalmember, which had been left at 23° C. under a relative humidity of 50%for seven days, and left at 60° C. under a relative humidity of 90% fortwo days. Then, the corrosiveness was observed. O represents thealuminum foil unchanged, and X represents the aluminum foil turnedwhite.

Light Leakage

Each of the optical members, which had been left at 23° C. under arelative humidity of 50% for seven days, was cut into a piece of 120 mm(in the MD direction of the polarizer)×60 mm and a piece of 120 mm (inthe TD direction of the polarizer)×60 mm, which in turn were attached toboth sides of a glass substrate to overlap each other, followed byautoclaving at 50° C. and at 5 kg/cm²×20 min. Then, each sample was leftat 80° C. for 120 hours and observed in appearance. The sample wherelight leakage was not detected is represented by O, and the sample wherelight leakage was detected is represented by X.

Durability

Each of the optical members, which had been left at 23° C. under arelative humidity of 50% for seven days, was cut into a piece of 120 mm(in the MD direction of the polarizers)×60 mm, and attached to a glasssubstrate, followed by autoclaving at 50° C. and at 5 kg/cm²×20 min.Then, the sample was left at 80° C. and at 60° C. under a relativehumidity of 90% for 120 hours, and observed in appearance. The samplewhere foam, looseness, or peeling was not found is represented by O, andthe sample where foam, looseness, or peeling was found is represented byX.

Adhesive Force and Adhesion to Substrate

Each optical member, which had been left at 23° C. under a relativehumidity of 50% for seven days, was cut into a piece of a width of 25 mmand attached to a glass substrate, followed by autoclaving at 50° C. andat 5 kg/cm²×20 min. Then, the sample was measured for adhesive force at23° C. under a relative humidity of 50% using a tensile tester at apeeling angle of 180 degrees and at a peeling rate of 0.3 m/minaccording to JIS Z0237, which regulates a method for testing an adhesivetape and an adhesive sheet. Further, the sample was also measured foradhesion to polarizer (substrate). The sample where the adhesive layerwas not completely peeled from the polarizer is represented by O, andthe sample where the adhesive layer was peeled from the polarizer isrepresented by X.

Contamination of Attachment Target

Before and after measuring the adhesive force, the contact angle wasmeasured on the surface of the glass substrate. The sample where thecontact angle of the glass substrate remained unchanged before and afterthe measurement is represented by O, and the sample where the contactangle of the glass substrate was changed before and after themeasurement is represented by X. Meanwhile, the contact angle wasmeasured according to JIS R3257, which regulates a method for measuringwettability of a glass substrate.

Low Temperature Stability

Each of the optical members, which had been left at 23° C. under arelative humidity of 50% for seven days, was cut into a piece of 120 mm(in the MD direction of the polarizers)×60 mm and attached to the glasssubstrate, followed by autoclaving at 50° C. and at 5 kg/cm²×20 min.Then, the sample was left at −40° C. for 120 hours and observed inappearance. The sample where foam, looseness, peeling, or a precipitatewas not found is represented by O, while the sample where foam,looseness, peeling, or a precipitate was found is represented by X.

Reworkability

A peeled state was observed during measurement of the adhesive force.The sample where an interfacial fracture was observed is represented byO, and the sample where cohesive fracture and/or sticking to the glasssubstrate (attachment target) were observed is represented by X.

As shown in Table 3, the adhesive layers of Examples 1 to 10 had asurface resistance of 10¹¹ Ω/cm² or less, and exhibited good antistaticproperties. Additionally, Examples 1 to 10 had a short gel fractionstabilizing period of 3 days. Further, the optical members of Examples 1to 10 had a suitable adhesive force of 4 to about 8 N/25 mm. Moreover,the optical members of Examples 1 to 10 exhibited good properties interms of all of metal corrosiveness, light leakage, durability, adhesionto substrate, contamination of attachment target, low temperaturestability, and reworkability.

On the other hand, as shown in Table 4, since Example 11 containedneither the hydroxyl group-containing (meth)acrylamide nor theantistatic agent, it had a surface resistance of 10¹⁵ Ω/cm², therebyshowing that Example 11 had lower antistatic properties than Examples 1to 10. Further, Example 11 had a gel fraction stabilizing period of 10days, which was longer than that of Examples 1 to 10.

Further, since Example 12 did not contain the hydroxyl group-containing(meth)acrylamide, it had a gel fraction stabilizing period of 10 days;which was longer than that of Examples 1 to 10.

Further, since Example 13 had a lower amount of the hydroxylgroup-containing (meth)acrylamide, it had a surface resistance of 10¹⁴Ω/cm², thereby showing that Example 13 had lower antistatic propertiesthan Examples 1 to 10. Further, Example 13 was evaluated as X in termsof durability and reworkability.

Further, since Example 14 had a higher amount of the hydroxylgroup-containing (meth)acrylamide, it was evaluated as X in terms ofdurability.

Further, since Example 15 had a lower amount of the hydroxylgroup-containing (meth)acrylamide, it was evaluated as X in terms ofdurability and reworkability.

Further, since Example 16 contained N,N-diethyl acrylamide which is amonomer containing a nitrogen group without containing a hydroxyl group,it had a gel fraction stabilizing period of 10 days, which was longerthan that of Examples 1 to 10, and was evaluated as X in terms of lightleakage and durability.

Next, embodiments will be described with reference to Examples 17 to 32.First, adhesive compositions according to Examples 17 to 32 wereprepared and applied to protective films, thereby producing surfaceprotective films of Examples 17 to 32. Then, performance of the surfaceprotective films was tested. A detailed description is as follows.

(Preparation of Copolymer Composition According to Example 17)

1 part by weight of hydroxyethylacrylamide as the (meth)acrylamidehaving a hydroxyl group, 40 parts by weight of butyl acrylate, 58.99parts by weight of 2-ethylhexyl acrylate, and 150 parts by weight ofethyl acetate as a solvent were introduced into a flask equipped with areflux condenser and an agitator, and were heated to 65° C. whileconducting nitrogen substitution. Then, 0.1 parts by weight of AIBN wasadded thereto and 0.05 parts by weight of AIBN as a polymerizationinitiator was added again thereto 1 hour thereafter, followed bypolymerization for six hours at 65° C. When the polymerization wascompleted, 0.01 parts by weight of 1-hexyl-3-methylimidazoliumhexafluorophosphate was added as an ionic compound, and 36 parts byweight of ethyl acetate was further added to adjust the viscosity,followed by cooling to room temperature, thereby producing a copolymercomposition solution containing the adhesive composition of Example 16.

The adhesive composition in the copolymer composition solution had aconcentration of 35 wt. %, and the copolymer composition solution had aviscosity of 3,500 mPa·s. Table 5 shows an ingredient ratio of theadhesive composition, a concentration of the adhesive composition in thecopolymer composition solution, and a viscosity of the copolymercomposition solution.

Further, the weight-average molecular weight of the base polymer wasmeasured by Gel Permeation Chromatography (GPC). Results are shown inTable 5.

(Preparation of Copolymer Composition Solutions According to Examples 18to 32)

Copolymer composition solutions containing adhesive compositions ofExamples 18 to 32 were obtained by the same process as that of Example17, except for the following: at least one of butylacrylate,2-ethylhexyl acrylate, 2-hydroxyethylacrylate, 4-hydroxybutylacrylate,acrylic acid and acryl amide with hydroxyethylacrylamide combined (notcombined) therewith as the hydroxyl group-containing (meth)acrylamidewas appropriately combined with ethyl acetate as a solvent, whilecombining (not combining) one of 1-hexyl-3-methylimidazoliumhexafluorophosphate, N-methyl-N-propylpiperidiniumbis(trifluoromethanesulfonyl)imide, 1-ethylpyridinium bromide and1-butyl-3-methylpyridinium trifluoromethanesulfonate as the ioniccompound therewith at the same time. Tables 5 and 6 show the ingredientratios of the adhesive compositions of Examples 18 to 32, the viscosityof each copolymer composition solution, the concentration of theadhesive composition in each copolymer composition solution, and theaverage weight molecular weight of the base polymer.

(Preparation of Surface Protection Sheets of Examples 17 to 32)

With respect to 100 parts by weight of the adhesive composition in eachof the copolymer composition solutions of Examples 17 to 32 listed inTables 5 and 6, hexamethylenediisocyanate (isocyanate crosslinkingagent, Coronate HX™, obtained from Nippon Polyurethane Industry Co.,Ltd) as a crosslinking agent (B) was added at the ratios listed inTables 7 and 8 and sufficiently mixed to prepare adhesive compositionsolutions. Each of the adhesive composition solutions obtained wasapplied to a separable PET film (Trademark: MRF 38, obtained fromMitsubishi Polyester Film Co., Ltd.) to a thickness of 25 μm afterdrying, and dried at 90° C. for 3 minutes to form an adhesive layerconsisting of the adhesive composition. Then, the adhesive layers andthe separable PET films were attached to PET protective films(Trademark: Lumirror S10#25, obtained from Tone Co., Ltd.), therebyproducing surface protection sheets of Examples 17 to 32, respectively.

As in Example 1, performance of each surface protection sheet was testedfor surface resistance, metal corrosiveness, contamination of attachmenttarget, and low temperature stability. Here, the performance test wascarried out by replacing the glass substrate with a polarizer as theattachment target. The performance test was carried out for adhesiveforce, adhesion to substrate, and transparency of adhesive layer asdescribed below.

Further, as in Example 1, the concentration of the adhesive compositionin each adhesive composition solution, and the viscosity, gel fraction,and period for obtaining a stabilized gel fraction for each adhesivecomposition solution were measured. Results are shown in Tables 7 and 8.

Adhesive Force and Adhesion to Substrate

Each of the optical members, which had been left at 23° C. under arelative humidity of 50% for seven days, was cut into a piece of a widthof 25 mm and attached to the polarizer, followed by autoclaving at 50°C. and at 5 kg/cm²×20 min. Then, the sample was measured for adhesiveforce at 23° C. under a relative humidity of 50% using a tensile testerat a peeling angle of 180 degrees and at a peeling rate of 0.3 m/minaccording to JIS Z0237 which regulates a method for testing an adhesivetape and an adhesive sheet. Further, the sample was also measured foradhesion to a protective film (substrate). The sample where the adhesivelayer was not completely peeled from the protective film is representedby O, and the sample where the adhesive layer was peeled from theprotective film is represented by X.

Transparency of Adhesive Layer

The transparency of each surface protection sheet, which had been leftat 23° C. under a relative humidity of 50% for seven days, was confirmedby the naked eye. The sample where the adhesive layer exhibited goodtransparency is represented by O, and the sample where the adhesivelayer had an unclear portion is represented by X.

As shown in Table 7, for the surface protection sheets of Examples 17 to26, the adhesive layers had a surface resistance of 10⁸ to about 10¹¹Ω/cm², and exhibited good antistatic properties. Additionally, thesurface protection sheets of Examples 17 to 26 had a suitable adhesiveforce of 0.1 to about 0.15 N/25 mm. Moreover, the surface protectionsheets of Examples 17 to 26 exhibited good properties in terms of all ofmetal corrosiveness, adhesion to substrate, contamination of attachmenttarget, low temperature stability, and transparency of adhesive layer.

On the other hand, as shown in Table 8, since the surface protectionsheet of Example 26 contained neither the hydroxyl group-containing(meth)acrylamide nor the antistatic agent, it had a surface resistanceof 10¹⁵ Ω/cm², thereby showing that Example 26 had lower antistaticproperties than Examples 17 to 26. Further, Example 27 had a gelfraction stabilizing period of 10 days, which was longer than that ofExamples 17 to 26.

Further, since Example 28 did not contain the hydroxyl group-containing(meth)acrylamide, it had a gel fraction stabilizing period of 10 days,which was longer than that of Examples 17 to 26.

Further, since Example 29 had a lower amount of the hydroxylgroup-containing (meth)acrylamide, it had a surface resistance of 10¹⁴Ω/cm², thereby showing that Example 29 had lower antistatic propertiesthan Examples 17 to 26.

Further, since Example 30 had a higher amount of the hydroxylgroup-containing (meth)acrylamide, it was evaluated as X in terms ofadhesion to substrate and transparency of adhesive layer.

Further, since Example 31 had a lower amount of the hydroxylgroup-containing (meth)acrylamide, it was evaluated as X in terms ofcontamination of attachment target.

Further, since Example 32 contained N,N-diethyl acrylamide, which is amonomer containing a nitrogen group without containing a hydroxyl group,it had a gel fraction stabilizing period of 10 days, which was longerthan that of Examples 1 to 10, and was evaluated as X in terms ofadhesion to substrate and contamination of attachment target.

As described above, embodiments may provide an adhesive composition thathas a short aging time resulting in high productivity and permits theformation of an adhesive layer exhibiting good antistatic performance,and an optical member and a surface protective film including the same.

Embodiments may provide one or more advantages relative to comparativeapproaches. A comparative approach might be to provide a separateantistatic layer on a flat display panel, e.g., a cholesteric liquidcrystal layer may be provided with a polarization member at one oreither side thereof, the polarization member including an antistaticlayer, a dichromatic polarizer, and a quarter wavelength plate. In animplementation, the flat display panel may be provided with anantistatic adhesive sheet that includes a base film, an antistatic layercontaining a quaternary ammonium salt, and an adhesive layer stacked inthis sequence. However, since the aforementioned techniques form theantistatic layer and the adhesive layer through separate processes, suchtechniques may have low productivity. On the other hand, if theantistatic agent is contained in the adhesive layer of the optical filmor surface protective film, the adhesive layer may have antistaticproperties, thereby eliminating the separate formation of the adhesivefilm and the antistatic layer. However, if a general adhesive layer isformed by coating an adhesive composition on the optical film or surfaceprotective film, there can be problems of insufficient antistaticproperties and productivity reduction resulting from a long aging timefor forming the adhesive layer.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of skill in the art thatvarious changes in form and details may be made without departing fromthe spirit and scope of the present invention as set forth in thefollowing claims.

What is claimed is:
 1. An adhesive composition for forming a peelableadhesive layer, the composition comprising: a copolymer (A), thecopolymer (A) being a copolymer of: a hydroxyl group-containing(meth)acrylamide (a1), the hydroxyl group-containing (meth)acrylamide(a1) including at least one of a hydroxyl group-containing acrylamideand a hydroxyl group-containing methacrylamide, the hydroxylgroup-containing (meth)acrylamide (a1) being represented by thefollowing formula: H₂C═C(R1)ACONHCH₂CH₂OH, in which: R1 is H or CH₃, Ais a linking group, the linking group being (COOCH₂CH₂)_(n),COOCH₂CH₂OOC—CH₂CH₂, or Compound 1 represented by Chemical Formula 1:

 and n is 1 or 2, and a (meth)acrylate (a2), the (meth)acrylate (a2)including at least one of an acrylic ester and a methacrylic ester, the(meth)acrylate (a2) including at least one of methyl (meth)acrylate,ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate,isobutyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl(meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate,isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl (meth)acrylate, methoxyethyl(meth)acrylate, ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate,phenoxyethyl (meth)acrylate, nonylphenoxy polyethylene glycol(meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, n-butylacrylate, and tetrahydrofurfuryl (meth)acrylate, wherein the copolymer(A) includes about 0.1 to about 10% by weight of the hydroxylgroup-containing (meth)acrylamide (a1) and about 50 to about 99.1% byweight of the (meth)acrylate (a2) based on a total weight of thecopolymer (A); and an antistatic agent (B), the adhesive compositionincluding about 0.01 to about 2.0% by weight of the antistatic agent(B), and the antistatic agent (B) including an ionic compound, wherein:the copolymer (A) is crosslinked, the copolymer (A) has a polystyreneconversion weight-average molecular weight of about 300,000 to about1,000,000 as determined by gel permeation chromatography, thecomposition has a gel fraction, at 3 days at 23° C. under a relativehumidity of 50%, of about 90 to about 100% as a crosslinking degree, thecomposition has an adhesive force of about 0.05 (N/25 mm) to about 0.2(N/25 mm) measured according to JIS Z0237, the ionic compound is atleast one selected from a pyridinium salt, an alkyl pyrrolidium salt,and N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide,and the composition provides an adhesive layer that has a sheetresistance of about 1×10⁸ to about 1×10¹¹ Ω/cm².
 2. The adhesivecomposition as claimed in claim 1, wherein: the adhesive composition isfor a surface protection sheet.
 3. The adhesive composition as claimedin claim 1, wherein: the adhesive composition is for a surfaceprotective sheet, and the copolymer (A) includes about 50 to about 99.1%by weight of 2-ethylhexylacrylate as the (meth)acrylate (a2) based on atotal weight of the copolymer (A).
 4. The adhesive composition asclaimed in claim 1, wherein: the adhesive composition is for an opticalmember.
 5. The adhesive composition as claimed in claim 1, wherein thecopolymer (A) has a glass transition temperature (Tg) of about 0° C. orless.
 6. A surface protection sheet, comprising: a protective film; andan adhesive layer formed on one or both sides of the protective film,the adhesive layer including the adhesive composition according toclaim
 1. 7. An adhesive composition for an optical member, thecomposition comprising: a copolymer (A), the copolymer (A) being acopolymer of: a hydroxyl group-containing (meth)acrylamide (a1), thehydroxyl group-containing (meth)acrylamide (a1) including at least oneof a hydroxyl group-containing acrylamide and a hydroxylgroup-containing methacrylamide, the hydroxyl group-containing(meth)acrylamide (a1) being represented by the following formula:H₂C═C(R1)ACONHCH₂CH₂OH, in which: R1 is H or CH₃, A is a linking group,the linking group being (COOCH₂CH₂)_(n), COOCH₂CH₂OOC—CH₂CH₂, orCompound 1 represented by Chemical Formula 1:

 and n is 1 or 2, and a (meth)acrylate (a2), the (meth)acrylate (a2)including at least one of an acrylic ester and a methacrylic ester, the(meth)acrylate (a2) including at least one of methyl (meth)acrylate,ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate,isobutyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl(meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate,isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl (meth)acrylate, methoxyethyl(meth)acrylate, ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate,phenoxyethyl (meth)acrylate, nonylphenoxy polyethylene glycol(meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, n-butylacrylate, and tetrahydrofurfuryl (meth)acrylate; wherein the copolymer(A) includes about 0.1 to about 10% by weight of the hydroxylgroup-containing (meth)acrylamide (a1) and about 50 to about 99.1% byweight of the (meth)acrylate (a2) based on a total weight of thecopolymer (A), and an antistatic agent (B), the adhesive compositionincluding about 0.01 to about 2.0% by weight of the antistatic agent(B), and the antistatic agent (B) including an ionic compound, wherein:the ionic compound is at least one selected from a pyridinium salt, analkyl pyrrolidium salt, and N-methyl-N-propylpiperidiniumbis(trifluoromethanesulfonyl)imide, the copolymer (A) is crosslinked,the copolymer (A) has a polystyrene conversion weight-average molecularweight of about 1,000,000 to about 2,000,000 as determined by gelpermeation chromatography, the composition has a gel fraction, at 3 daysat 23° C. under a relative humidity of 50%, of about 50 to about 80% asa crosslinking degree, and the composition provides an adhesive layerthat has a sheet resistance of about 1×10⁸ to about 1×10¹¹ Ω/cm².
 8. Asurface protection sheet, comprising: a protective film optical sheet;and an adhesive layer formed on one or both sides of the optical sheet,the adhesive layer including the adhesive composition according to claim7.